/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.runners.core;



import com.bff.gaia.unified.sdk.transforms.windowing.BoundedWindow;

import com.bff.gaia.unified.sdk.values.PCollectionView;



import javax.annotation.Nullable;



/**

 * The interface to objects that provide side inputs. Particular implementations may read a side

 * input directly or use appropriate sorts of caching, etc.

 */

public interface SideInputReader {

  /**

   * Returns the value of the given {@link PCollectionView} for the given {@link BoundedWindow}.

   *

   * <p>It is valid for a side input to be {@code null}. It is <i>not</i> valid for this to return

   * {@code null} for any other reason.

   */

  @Nullable

  <T> T get(PCollectionView<T> view, BoundedWindow window);



  /** Returns true if the given {@link PCollectionView} is valid for this reader. */

  <T> boolean contains(PCollectionView<T> view);



  /** Returns true if there are no side inputs in this reader. */

  boolean isEmpty();

}